Sugar and cancer: unpacking the evidence

Berna Harmse picks up on the sugar and cancer dispute.

Researchers are continuously investigating the connection between sugar and cancer. Unfortunately, the topic causes a lot of anxiety and misinformation in the media and on the internet. There is no strong evidence that directly links sugar to increased cancer risk, but there is an indirect link.

What is the indirect link?

All the cells in our body, including cancer cells, need sugar (glucose) from our bloodstream for fuel. We get this blood glucose from carbohydrate-containing foods, including fruit, vegetables, starch, wholegrains and dairy. Some glucose is also made in our bodies from protein. 

Sugar doesn’t make cancer grow faster. As stated in a Mayo Clinic article, “All cells, including cancer cells, depend on glucose for energy. But giving more sugar to cancer cells doesn’t speed up their growth. Likewise, depriving cells of sugar doesn’t slow down their growth.”

Eating high-sugar foods increase our body weight and body fat, which is linked to some kinds of cancer. For that reason, the American Institute for Cancer Research recommends increased intake of wholegrains, vegetables, fruit and beans; and reducing intake of sugary beverages and sweets.

Influence on weight and metabolism

Let’s look at the influence on weight and metabolism. The Academy of Nutrition and Dietetics reinforces that much research shows that higher insulin (a hormone) levels and related growth factors may influence cancer cell growth the most, as well as increasing the risk for other chronic diseases. 

Different types of cancer cells have high amounts of insulin receptors, making them respond more than normal cells to insulin’s ability to promote growth.

All the food we eat gets broken down to smaller bits, in the process we call digestion. Glucose sits in the veins, and insulin working like a key, unlocks the veins so the energy can get to the rest of the body to be used. 

When insulin levels are high, it is a signal to the body that there is plenty of food available, and that these kilojoules should be used to grow and build reserves for future times of starvation.

Insulin levels rise quickly when we eat unrefined carbohydrates (white bread and sweets) and leads to a drop in blood glucose levels. Low blood glucose is the biggest appetite stimulant in the world. It makes you overeat, which again causes a release of more insulin and thus a cycle of eating more and gaining weight and body fat continues. 

Inactivity and being overweight also increases insulin levels, and so insulin resistance is caused. If no intervention is launched at this stage, diabetes soon follows.

Is there a link between cancer and diabetes?

Research is being done to investigate the direct link between cancer and diabetes, with some researchers speculating that the underlying metabolic factors, like long-term stress and the inflammation that comes with it, underpins some of the patterns behind it.

So, what do I eat considering all this information?

If you can keep your food portions controlled and maintain your weight, you are on the right track.

  • Avoid refined carbohydrates, like take-aways, white bread products, and sweetened foods and beverages. Rather choose high-fibre carbohydrates, like wholegrains, fruit, vegetables and legumes. Higher fibre foods are the cornerstone of blood glucose management.
  • The five-a-day approach is still best – try to have at least two fruits and three vegetables per day, or vice versa. This ensures the adequate intake of antioxidants which plays a big role in terms of fighting and preventing chronic diseases.
  • Vegetables and salad should take up half of your dinner plate, and carbohydrate and proteins should be the side dishes of the meal.
  • Try to have breakfast every morning and do not skip meals
  • Aim to do some form of physical activity most days of the week.

 

Berna Harmse is a private practicing dietitian. She holds a MSc in Dietetics, 
and has a special interest in oncology nutrition. She is also an external lecturer at Stellenbosch University Division of Human Nutrition.

MEET OUR EXPERT – Berna Harmse

Berna Harmse is a private practicing dietitian. She holds a MSc in Dietetics,


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